The invention relates generally to inspection systems and more specifically to radiographic inspection techniques and assemblies.
Typically, for certain radiography systems, X-rays are transmitted through an object and converted into light of corresponding intensity using a light production layer. The light generated by the light production layer is provided to an electronic device. The electronic device is adapted to convert the light signals generated by the light production layer to corresponding electrical signals. The electrical signals are then used to construct an image of the object.
In radiography, X-ray scatter undesirably reduces (or fogs) the resulting image. To control scatter for medical systems, lead grids are used on the detector to provide geometric rejection of the scattered, secondary X-rays. However, for non-destructive testing applications, higher energy X-rays are used, so grids are not always adequate. In a non-destructive inspection industrial environment, Compton scatter from an object can be a large part of the X-ray flux impinging on the X-ray film cassette. To reduce the scatter, a metallic plate or screen may be employed, to filter the lower energy Compton scattered radiation.
Furthermore, the film can be further intensified by the photoelectrons emitted from the metallic plate when the plate is in intimate contact with said film. This enables a high spatial transfer of the X-ray pattern to the film. In nondestructive testing at X-ray energies above 150 kV, this is the primary mechanism for darkening the film, as the film is essentially transparent to X-rays in this regime. A similar benefit is experienced with computed radiography, where metal screens are placed in intimate contact with the computed radiography image plates. In digital radiography, metal screens have been placed on the back surface (the side toward the X-rays) of X-ray phosphor screens, especially under X-ray energies of 1 MeV and above. In such an embodiment, the phosphor is typically viewed by a digital or analog camera.
It would be desirable for the metallic plate or screen to shield the electronic device from impinging X-rays. However, the metallic plate or screen may not provide the desired electron intensification and scatter rejection in the MeV energy range. Thus, in typical radiography systems, the metallic plate or screen is of higher thickness to provide the required shielding while maintaining the intensification benefits.
Therefore, it is desirable to develop a compact detector assembly that is capable of producing high quality images with enhanced contrast, while also reducing and controlling scatter.